This invention relates to medical test devices, methods and systems, and more particularly to devices, methods and systems for consistently and accurately measuring and mapping cardiac function, and simultaneously delivering electrical energy to the heart.
The heart is composed of a specialized system of cells that generate and conduct electrical impulses; it is these cells which are responsible for propagating muscle contraction, thus facilitating the pumping function of the heart. While over 90 percent of the heart""s mass is comprised of muscle fibers, the remaining specialized conduction tissues are distributed throughout the heart in order to enable contraction to be well synchronized. The heart is comprised of 4 chambers: 2 atria and 2 ventricles. Normally cardiac impulses are generated in the sino-atrial (SA) node, located in the right atrium. The signals then pass to the left atrium, and down the bundle of His towards the left and right ventricular bundles. Once arriving at these bundles, the impulse is distributed throughout the ventricles, enabling them to contract, thus pumping blood throughout the pulmonary and systemic circulations. The ventricles are capable of initiating an impulse if the normal SA pathway is disrupted, albeit at a much slower rate. Deviations from the normal pattern often lead to a variety of symptoms, and can predispose the patient to several serious clinical problems including sudden cardiac death (SCD). Problems with the cardiac conduction system are frequently called arrhythmias or dysrhythmias. Dysrhythmias in which the heart beats too slowly often require a pacemaker to raise the rate to more physiologic levels. Ventricular dysrhythmias whereby the heart beats too rapidly, often called tachycardia, can devolve into a life threatening emergency called ventricular fibrillation, which requires defibrillation to treat.
A variety of cardiac disease processes can contribute to the heart beating too slowly to provide appropriate cardiac output. When this occurs, often a pacemaker is required to reestablish proper heart rate. Cardiac pacing, or electrostimulation, involves sending signals from an electrical generator to the heart in order to initiate or sustain a heart rate that is physiologically appropriate. There are a variety of methods to apply such technology, including transthoracic, thransvenous and permanent pacemakers. Transcutaneous pacemakers involve placing electrodes on the skin of the patient, usually one on the chest, and one on the back, in order to deliver high energy impulses. This method is usually reserved for emergency pacing.
In the majority of patients dying suddenly from sudden cardiac death (SCD), primary electrical failure occurs, usually in the form of ventricular fibrillation. Fibrillation is chaotic, asynchronous electrical activity of the heart. The impulse in this dysrhythmia spreads erratically along a variety of changing pathways, instead of originating from a single site, usually the SA node, and then spreading in a highly ordered manner. These fibrillatory impulses result in the different regions of the heart muscle being depolarized randomly in relation to the other areas of the myocardium. Because there is simultaneous relaxation and contraction of the heart muscle cells, depending upon their relation to the fibrillation impulses, there is complete disruption of ventricular contraction, and the loss of pump function. Circulatory collapse ensues, unless rapid and appropriate advanced cardiac life support (ACLS) is initiated.
ACLS involves supplementing basic cardiopulmonary resuscitation with additional interventions, including electrocardiographic monitoring and external pacemaker devices or defibrillation. Successful treatment of patients in ventricular fibrillation depends upon reaching the patient early in the event, and initiating definitive therapy rapidly. Once on the scene, one of the rate limiting steps is the 2 step process of applying electrodes to monitor for the dysrhythmias to define the cardiac mechanism, then applying the defibrillation paddles to deliver the charge to the patient""s heart.
Electrical defibrillation is a method used to terminate ventricular fibrillation. It can also be used to terminate atrial and ventricular tachydysrhythmias. The procedure involves placing two paddle electrodes on the chest, and delivering a high-energy shock wave to the heart. If the shock energy is sufficiently powerful, it will depolarize the heart cells, allowing the sinus node to resume initiating cardiac impulses in a more coordinated manner. The objective is to use the lowest amount of energy possible. Unfortunately the large electrode area and skin resistance create the need for larger amounts of energy to be used, which predisposes the patient to discomfort and bums. The energy required to terminate ventricular fibrillation is between 200-400 Joules, depending upon the underlying cardiac pathology, the body habitus of the patient, and the orientation of the heart within the chest cavity. More energy is required to overcome size and resistance. The energy of the electrical discharge can cause myocardial injury.
The process of defibrillation is subject to similar procedural and anatomic problems found in obtaining electrocardiograms (ECG or EKG). The current state of the art involves placing 2 electrodes on the patient""s chest. It is well known that fibrillatory signals do not propagate in a coordinated or linear manner simplistically as north to south, left to right. Also, we know resistance to the delivered shock is patient dependent.
It is widely accepted that the success of scientific testing and therapeutic interventional procedures is based upon two criteria: 1. Reproducibility, and 2. Accuracy. Nowhere are these more critically essential than in medicine, especially cardiology, where lives often hang in the balance relying on the results.
The EKG has long been an important diagnostic tool in the field of cardiology. The EKG is used to measure the timing and amplitude of the electrical signal from the subject""s heart, presenting the measurements as a visual display. The standard xe2x80x9ctwelve-leadxe2x80x9d EKG involves the separate placement on the patient""s body of ten individual electrodes, six precordially and one each on each of the four limbs. The ten electrodes are attached one at a time and must each be placed over a specific point on the patient""s body. If any of the precordial electrodes are mixed up with each other, or if the arm or leg electrodes are swapped over, the EKG tracing obtained will be faulty.
The six precordial electrodes are placed on the patient""s chest at specific recording zones over the heart. V1 is properly positioned in the fourth intercostal space to the immediate right of the sternum. V2 is also located in the fourth intercostal space, but to the immediate left of the sternum. V4 is positioned in the fifth intercostal space at the midclavicular line. V5 and V6 are similarly located in the fifth intercostal space, but at the anterior axillary and midaxillary lines respectively. Finally, V3 is positioned midway between V2 and V4.
The process of obtaining an EKG tracing is fraught with potential errors. In particular, the technician may make mistakes either in placing the electrodes or in reading the tracing. This is particularly likely in an emergency situation, when the test often must be administered in a hurry and the patient is frequently sweaty, immobile, and minimally cooperative. Further variability and error, in the form of discordant respiratory artifact, is introduced due to the fact that the six precordial electrodes move independently with the patient""s respiration, causing noise or spurious signals. Similarly, error is introduced into EKGs performed during stress testing due to the independent motion of the six precordial electrodes, leading to multiple discordant body motion artifact (BMA).
In particular, many studies support the fact that there is a lack of reproducibility in EKG tracings obtained for the same patient due to variations in electrode placement, resulting consequently in errors in test interpretation and even in potential misdiagnosis. [See, e.g., Herman, Michael V. et al.,xe2x80x9cVariability of Electrocardiograph Precordial Lead Placement: A Method to Improve Accuracy and Reliability,xe2x80x9d Clin. Cardiol., Vol. 14, pp. 469-476 (1991).] Since today""s EKG machines now handle most of the measurement and recording functions electronically, placement of the electrodes is normally the principal variable subject to error in the administration of the test. Many times patients are even subjected to unnecessary hospital stays because it is impossible for the physician to determine whether observed EKG variation is due to ischemia or merely to a different electrode position. Some cardiologists even routinely ignore the results of certain electrode leads that are frequently misplaced, such as V3, which actually provides one of the key views of the heart. Standardization of measurement conditions is therefore critical to the usefulness of this important diagnostic tool and represents a long-felt need in the field for an easily applied, clinically practical device to solve this problem.
The need for manual placement of each electrode has other effects on the usefulness and efficiency of the EKG test. Among other things, placement of the electrodes takes a considerable amount of time, often constituting the rate-limiting step in obtaining the tracing. One estimate is that it takes on average seven minutes to place the six precordial leads for a standard EKG test. Since the average 250 bed hospital may do over 100 EKG tests per day, a lot of technician time is consumed by doing this repetitive task, time that could be beneficially devoted to other activities. This waste of time is particularly apparent in a hospital situation where the same patient will often have multiple EKG tests done in a short period of time. On average a cardiac patient admitted for four days will have at least seven EKGs (more often than not, greater than ten), and each time the electrodes must be manually repositioned. Time is also consumed, of course, each time an EKG must be repeated due to poor electrode placement, and this loss is further compounded by the fact that the cost of the repeat test may not be billable to the patient""s insurance provider because it was required due to the hospital""s error.
Another problem frequently encountered during the administration of an EKG test utilizing conventional precordial electrodes is that the self-adhesive disposable xe2x80x9cstickiesxe2x80x9d with which the precordial electrodes are generally manually applied are good for only one test administration and are easily dislodged and/or ruined. This means that replacements are frequently required, often up to several per patient per test. This can add up over time to a significant expense for the hospital, an expense that often cannot be passed through to the patient""s insurance provider. Similar problems with electrode dislodgement occur when suction cups are used to apply the electrodes, particularly where the patient has large pectoral muscles or breasts, has a hairy chest, is sweaty, or the test is performed with the patient partially or completely sitting up. Other problems with the current method of EKG electrode placement include the difficulty in, and time required for, cleaning the electrodes and/or suction cups between patients, and the potential for entanglement, or even misconnection, of the individual electrode wires. The latter problem is particularly significant because each electrode must be connected to a specific wire that in turn must be connected to a specific input on the EKG machine or the tracing obtained will not be accurate.
Although the prior art teaches several approaches to solving various of the above-described problems that have long been encountered with the conventional twelve-lead EKG electrode system, none of the systems described allow complete freedom and guidance for the accurate and independent positioning and attachment of all six precordial electrodes when the test is initially performed on a particular patient, in conjunction with complete reproducibility of results for all future EKGs on that patient without the need for individual repositioning of the electrodes each time the test is performed. For example, in Rollman et al., U.S. Pat. No. 5,370,116, three of the precordial electrodes are completely fixed on a platform, while the other three are independently moveable but attached via leads rather than being resident on the platform. Therefore, although allowing some freedom of adjustment of electrode position, Rollman et al. do not teach an apparatus or method that allows all electrodes to be independently positioned during the first use and then be locked into that position to ensure consistent reproducibility of future test results.
Similarly, in Rubin, U.S. Pat. No. 4,854,323, all six precordial electrodes are independently positionable along a platform, after which each is held in place on the platform by a clip. However, the electrodes of Rubin cannot be locked into place in a permanent manner, as the clips may be easily jarred and dislodged or even be subject to accidental or deliberate tampering. Further, the platform of Rubin is necessarily made of a semi-rigid material that will hold the shape into which it is bent, otherwise the electrodes cannot be properly positioned on the patient""s torso. Besides the fact that this design provides no guidance to the technician for the proper positioning of the electrodes, the need to use a semi-rigid material for the platform creates a serious drawback in that the platform is not able to properly accommodate patient movement or respiration without loss of electrical contact. This problem in turn may lead to seriously inconsistent EKG test results. What has been needed, therefore, is a completely reusable and accurate patient-specific EKG electrode system that must be fitted to a particular patient only once, after which the system may be consistently, accurately and repeatedly reused for that patient without remeasurement or precordial electrode repositioning.
Accordingly, a primary object of the present invention is to provide an easy-to-use way to consistently map and measure cardiac function.
In particular, an object of the present invention is to provide a way to reliably and consistently map and measure the cardiac function of a particular patient at any number of spaced time intervals.
A further particular object of this invention is to provide a way to quickly and accurately map and measure the cardiac function of any patient.
Another particular object of this invention is to provide a patient-specific EKG electrode set that may be reliably and conveniently reused any number of times to provide consistently reproducible measurements for a particular patient.
An additional particular object of the invention is to provide a set of EKG electrodes that may be quickly and easily attached to any patient in the proper positions.
A further particular object of this invention is to provide an easy-to-use and consistently positionable electrode system that can be used for either left- or right-sided operation.
Additionally, it is desired to have a flexible electrode platform that can be used for both EKG testing and the delivery of therapeutic electrical impulses.
A patient-specific EKG electrode platform and positioning system allows the standard twelve-lead EKG test to be performed in a more accurate, consistent, and reproducible manner by eliminating individual positioning of the six precordial electrodes for all but the first test on a particular patient. A platform for mounting and positioning electrodes is configured to allow the precordial electrodes to be aligned in the optimum manner for the performance of the EKG test. Each of the six precordial electrodes V1-V6 is mounted on the platform via a moveable mount slidably attached to the platform.
After the platform has been properly aligned on the torso of the patient, the mount containing each electrode is moved until it is properly positioned for the test. The position of each electrode and its respective mount is then permanently fixed utilizing a lock-down mechanism that can also serve to create a connection between the electrode and a wire lead connectable to the EKG machine. All six precordial electrodes are thereafter accurately and permanently positioned on the platform so that when the platform is subsequently aligned properly on a particular patient""s torso, all six electrodes will be properly and consistently positioned for a repeat administration of the EKG test on that patient without need for readjustment of the individual electrodes. The now patient-specific platform may be aligned properly on the patient during subsequent tests by utilizing an index marker that was marked or physically shortened during the initial alignment of the platform to match up with a selected anatomical reference point.
This same platform may be simultaneously or sequentially used for delivering appropriate energy to the heart for external pacemaker therapy, cardioversion of tachydysrhythmias, and emergency defibrillation, since the platform is in the proper position for transmitting current to each of the six precordial electrodes. This will eliminate one of the time wasting steps in ACLS: delivering the shock, removing the paddles and awaiting the monitor to recapture the signals.
Changing the orientation of the delivery electrodes or paddles can decrease the level of energy delivered to the patient, while sending such shocks in a manner that more likely will surround the fibrillatory impulses. The platform of the present invention will deliver the therapeutic shock in a more physiological orientation than the current point A to point B methodology. Because each individual is different, the platform can be manipulated to align properly on any patient. The consistent cardiogram platform enables the current to flow from several precordial positions, paralleling the major vectors of signal impulse as reflected on the EKG.
The present invention can also improve the manner in which therapeutic electrical impulses are delivered. Typically the energy is sent to the patient simultaneously through two electrodes. The underlying heart cells are in various stages of refractoriness. Since the platform of the present invention has electrodes located near the SA node, the AV node, parallel to the bundle of His, and the left/right bundle branches, it is reasonable to deliver therapeutic electrical stimulation sequentially through the electrodes instead of simultaneously, thus facilitating a more physiologic cardiac response. Therefore, in addition to sending the signal simultaneously through all the electrodes, the therapeutic electrical impulses can alternatively be delivered sequentially delayed from V1 and V2 to V3 to V4 through V6 in a manner that simulates the temporal sequence of the normally functioning heart. Either way, the platform of the present invention focuses the impulse to several points of the heart in a more targeted and precise manner. This is termed herein xe2x80x9casynchronous defibrillation,xe2x80x9d which is a component of the general concept known as xe2x80x9casynchronous therapeutic electrostimulationxe2x80x9d as it applies to tachydysrhythmias and bradydysrhythmias.
The phrase xe2x80x9casynchronous defibrillationxe2x80x9d includes sequentially delivering therapeutic electrical stimulation in addition to utilizing the present methodology of simultaneous electrical stimulation. The platform of the present invention offers a larger enveloping electrode zone around the fibrillatory area. Using integrated software, the strength of the fibrillatory waves within each electrode coverage area can be interpreted. Subsequently, and simultaneously or sequentially, therapeutic impulses would be sent at specifically tailored energy levels and tailored energy burst times through each electrode. The level of energy sent would be sufficient to overcome the fibrillation, but compared to the global high energy approach currently delivered through the 2 lead system, the levels used could be lower, thus reducing burns, discomfort, and myocardial injury.
The same rationale would apply to pacemaker therapy. It is well known that capture and propagation of a signal by the underlying heart is critical to successfully establishing an appropriate heart rate transcutaneously. The energy requirement to effectively pace a heart through the existing 2-electrode technology often is very uncomfortable for the patient. The platform array could take advantage of the same physiological considerations in cardiac pacing as in cardioversion, since altering the location of the electrodes to a more physiologic orientation may allow lower energy to achieve the same results. The asynchronous timing option may offer an advantage of paralleling the normal physiologic impulse propagation of the heart.
The present invention offers a significant improvement on the monitoring and treatment of the cardiac patient, especially the sudden cardiac death victim, and patients with symptomatic brady-dysrhythmias and tachy-dysrhythmias.
In a preferred embodiment of the invention, a flexible plastic precordial electrode platform has a xe2x80x9creversed Sxe2x80x9d shape and embedded wires accessible at one end of the platform for connection to the EKG machine and to a source of electrical impulses. The precordial electrodes V1-V6 are mounted on the undersides of plastic electrical connectors that are mounted around the precordial electrode platform in a manner that allows each electrode to initially be freely moveable horizontally along the length of a section of the platform. Once each electrode is properly positioned, the electrical connector on which it is mounted is activated by compressing the plastic connector body around the platform, simultaneously fixing the electrode in place and making an electrical connection between the electrode and two of the embedded wires.
It is normally desirable to utilize one or more limb electrodes in conjunction with the precordial electrode platform, and any of a number of standard implementations may be used. A cabling device may be employed as a convenient method of connecting the precordial electrode platform, and possibly the limb electrodes, to the EKG machine. A further option is the inclusion of standard telemetry devices on each connector to transmit signals to the EKG machine or some other measurement device, either instead of or simultaneously with transmission of signals through the regular electrode wiring, the latter allowing both the standard telemetry test and the 12-lead EKG to be taken at the same time with the same device. This embodiment of the invention may also be easily configured for use in a right-sided EKG test by reversing the platform horizontally, flipping over the connectors, and replacing the connectors on the platform so that each electrode is again in contact with the torso of the patient.
In an alternate embodiment of the invention, the totally integrated precordial electrode platform has multiple articulating or telescoping arms, particularly adapted for folding or collapsing the device for transport and storage. The electrodes are independently mounted via mounting pads on the movably connected arms and each may be freely adjusted along its respective arm until it reaches the proper alignment, after which it is fixed into the proper position by serrations, teeth, or other ridge-like protrusions present along the surface of each arm.
In an additional embodiment of the invention, the patient retains the patient-specific device after initial setup in a carrying case that holds the device, various optional accessories, and relevant informational materials. In the preferred embodiment, the case is made from molded plastic, having a built-in carrying handle. The carrying case has a well shaped and sized to hold the precordial electrode platform of the invention without damage to the wires or electrode mounts, with one or more additional wells optionally provided to hold various optional accessories, such as a set of limb electrodes or a cabling device. The case may optionally also hold informational accessories and materials, such as a base-line EKG tracing for the patient taken using the patient-specific precordial electrode platform, a Patient Information card, disease management pamphlets or records, and instructional materials for use of the electrode platform.
The method of cardiac mapping and measurement utilizing the electrode positioning device of the present invention begins with proper alignment of the precordial electrode platform on the patient. The alignment is permanently adjusted by marking or altering the index device and each electrode is then properly positioned and locked into place. The four limb leads are next attached to the patient, and the leads from the precordial electrodes and limb leads are all connected to the EKG and source of electrical energy. The EKG test and delivery of therapeutic electrical impulses are performed in the normal manner, after which the electrode leads are disconnected from the machines and the limb electrodes and precordial electrode platform are removed from the patient and saved for future use. For subsequent administration of the EKG test and delivery of therapeutic electrical impulses, except for simple alignment of the precordial electrode platform previously setup for the patient on that patient, no adjustment of electrode position is necessary, with the technician proceeding straight to attachment of the limb leads, followed by connection of the leads to the machine and performance of the procedures. A completely accurate and consistently reproducible EKG result and delivery of electrical impulses to targeted spots are therefore obtained with minimal setup time.